The present invention relates to the medical diagnostic imaging arts. It finds particular application in conjunction with computerized tomographic (CT) scanners and fluoroscopy systems and will be described with particular reference thereto. However, it should be appreciated that the present invention may also find application in conjunction with other types of imaging systems and applications where volumetric imaging data is acquired.
Conventional, single detector ring, axial computerized tomography (CT), and its extensions, such as spiral CT and multiple detector ring CT, are well known and documented. In all these cases, multiple individual radiation detector elements, or small arrays of detector elements, are mounted on an inside cylindrical surface of the gantry, to form one (in the case of conventional CT), or a small number of rings (in the case of multi-slice CT). In some scanners the detectors are mounted on arc segments that rotate with the gantry.
An x-ray source emits a thin, highly collimated x-ray fan beam. Rotation of the gantry is typically continuous, with one or a few CT slices acquired with each revolution. Data from larger volumes are acquired by either indexing the patient in steps, synchronized with the gantry rotation (in the case of conventional CT), or continuously (in the case of spiral CT), along the center line of rotation and acquiring one or a few CT slices with each revolution.
Alternatively, volume CT data has been acquired with limited success, by mounting image intensifier-based fluoroscopic cameras on CT-gantry type frames. Such a system is described in a paper presented at SPIE Medical Imaging Conference on Feb. 24, 1997, by R. Ning, X. Wang and D. L. Conover of Univ. of Rochester Medical Center. The major disadvantage of this approach lies in the geometric distortion inherent to image intensifiers. Before a volume CT reconstruction can be performed, all video data has to be processed through an extremely tedious geometric correction algorithm, and even this is only partially successful, as the geometric distortion is typically dependent on the orientation, in space, of the image intensifier and thus the distortion pattern changes as the gantry rotates.
Further disadvantages of this concept lie in the veiling glare characteristic of image intensifiers, which reduces object contrast and causes reconstruction artifacts, and in the poor spatial resolution of image intensifiers. Because of the difficulty of reconstructing volume CT from image intensifier image data, and also because of the size and weight of image intensifier cameras, practical application of this concept has been virtually non-existent.
U.S. Pat. No. 5,588,033 discloses a third method for acquiring volume CT data, which involves the use of individual sheets of photographic film to acquire images at a series of angles through a patient. This method overcomes the limitations of image intensifier geometric distortion, but is extremely cumbersome due to the need to take individual photographic images that have to be developed and scanned into a computer for CT reconstruction processing. In practice, this limits the number of projections that can be acquired per examination, and thus limits the quality of CT image data that can be obtained. Such a procedure also takes a long time, during which the patient has to remain completely stationary.
Accordingly, it has been considered desirable to develop a new and improved method and apparatus for acquiring volumetric computer tomography image data using a flat panel matrix image receptor which meets the above-stated needs and overcomes the foregoing difficulties and others while providing better and more advantageous results.